Power tools such as chainsaws and hedge trimmers can operate at a constant speed and torque. For example, a chainsaw drives a cutting chain at a constant speed (measured in revolutions per minute) around a blade. The cutting chain is communicated around the blade by a sprocket that is attached to an output spindle. The output spindle is rotated by a motor, which causes the sprocket to rotate. The motor can include an electric motor or an internal combustion engine. Rotation of the output spindle and sprocket cause the cutting chain to operate at a constant speed and cause teeth of the cutting chain to impart torque to cut into a work piece.
Some cutting operations benefit from higher speed and lower torque settings for a power tool. For example, if a user desires to cut a soft wood work piece and the work piece is thick, a higher speed and lower torque is useful because the lower torque may reduce tearing of the work piece, while the higher speed will allow the user to cut through the thick work piece more quickly.
Some cutting operations and power tools benefit from operating at a lower speed. For example, some power tools incorporate a battery that is used to power an electric motor. When operating at a constant speed and torque the power tool will exhaust the battery within a given period of time. The ability to reduce the speed of the power tool in certain contexts will increase operating time of the tool by reducing battery usage.